Ch. 7 Bones c
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What is the word for the formation of bone? What are the two methods that bone develops in a human fetus/infant?
Ossification. The two methods are intramembranous ossification and endochondral ossification
What are the materials used in each form of the respective ossification and what kind of bone does each form?
Intramembranous ossification uses fibrous membranes and forms flat bones. Endochondral ossification uses hyaline cartilage and forms most of the rest of the bone.
When does endochondral ossification begin and when does it end?
Around 8th week of utero and continues until about age 18 to 20
What triggers ossification to begin? Where and when does it begin?
The hyaline cartilage shaft is permeated by blood vessels allowing stem cells to enter and turn into osteoblasts. Begins between weeks 8 and 9 in embryo.
What is the first step of Endochondral ossification?
- A bone collar is formed. Osteoblasts secrete osteoid along the hyaline cartilage shaft diaphysis, encasing it into bone. This is the bone collar.
What is the second step in endochondral ossification?
- While the bone collar is forming, chondrocytes within the collar signal to the surrounding matrix to calcify. Chondrocytes die, leaving cavities.
What is the third step in endochondral ossification?
- Month 3 in utero. A periosteal bud (nutrient artery and vein, lymphatic vessels, nerve fibers, osteoblasts/clasts) invades the cavities. The osteoclasts partially erode the calcified matrix. Osteoblasts secrete osteoid around the remaining hyaline cartilage fragments, forming trabeculae and ultimately spongy bone.
What is the fourth step in endochondral ossification?
- 3 months to birth. The hyaline cartilage model elongates by division of cells. Ossification chases this elongation as the cartilage calcifies and so on. Osteoclasts break down the calcified matrix and form the medullary cavity.
What is the fifth step in endochondral ossification?
- Shortly before or after birth. The same thing that happened in the diaphysis (bone formation) now happens in the center of the epiphyses, except no bone collar is made and no medullary cavity is formed.
Where is hyaline cartilage left after step 5 of endochondral ossification?
epiphyseal surfaces (articular cartilage) and between diaphysis and epiphysis (epiphyseal plates). By late teens to early 20’s this cartilage is consumed and bone can no longer grow in length.
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